Some advocates of the UFO phenomenon argue that the origin of UFOs is from a parallel universe. Science, has of late, discussed the concept of parallel universes as just, that a concept. However, there may be more to it than that.
In an opinion interview between physicist Brian Greene and writer Amanda Gefter in "New Scientist" magazine, volume 209 number 2798 dated 5 February 2011, Greene says "We have no concrete evidence today of parallel worlds. But there are multiverse scenarios in which we might have access to other universes...I'm particularly fond of the brane multiverse, which is the idea from string theory that we may be living on a membrane that is floating in a higher dimensional space. I think there's a chance that we may test it shortly."
Greene's new book is titled "The Hidden Reality" published 2011 by Alfred A Knopf. ISBN 978-0-307-26563-0 (click here for more on the book.)